The present invention relates to connection blocks for telephone instruments. More particularly, the present invention relates to improved telephone instrument connection blocks which provide finite test conditions and signals emulative of a field troubleshooter's tests in automatic response to signals sent from a central office test board.
Recent developments and trends in the telephone art have created a desire and need to minimize the use of field service men and troubleshooters. On one hand, the telephone utilities have relied increasingly upon telephone subscribers to pick up their telephone instruments from a centralized telephone service store and connect them for use at the home or office by plugging into permanently installed modular jacks. By relying upon the customer to make the field installation, the utilities have entirely eliminated the need to dispatch an installer, thereby realizing substantial savings in the cost of providing newly requested service. Nevertheless, customers have often misconnected the equipment with the result that expensive troubleshooters have still been dispatched for field testing to locate and correct such problems. Consequently, a need has arisen to be able to ascertain from a test board usually provided at the telephone company's switching equipment in a central office whether a faulty line condition results from a misconnected instrument or from a true defect in the line itself.
On the other hand, governmental regulatory agencies have become increasingly liberal in allowing telephone customers to purchase telephone instruments of widely varying makes and models on the open market and connect them directly to the telephone utility's lines by plugging into the permanently installed modular jacks. In such cases, the need has often arisen to be able to test the entire line before informing the customer that the instrument is either misconnected to or incompatible with the utility's lines or central office equipment.
In an attempt to meet the needs for remote disconnect, several proposals have been made to apply momentary test voltages to charge capacitors and actuate relays at the station protector of the customer service drop. Such prior devices were described in an article entitled "Subscriber Disconnect Units" appearing in the May 1, 1978 issue of Telephone Engineer & Management at pages 94-96. The units described in that article have a number of disadvantages and drawbacks overcome by the present invention. First, the units disconnected at the station protector of the customer service drop and failed to test the wiring inside the homes or office up to the point of the modular jack. Second, and perhaps of even greater significance, such prior art remote disconnect units did not provide a metallic short across the tip and ring wires during a first portion of a test interval, and an open condition during a second portion of the test interval. Third, such prior devices became actuated immediately upon application of the test voltage rather than waiting until all voltages were removed from the line undergoing test and it became quiescent which limited useful loop length of such devices.
Still another problem has remained unsolved by the prior art remote disconnect units. This problem is testing the quality of the line from the service instrument connection block to the central office. In specialized applications such as remote broadcast and data transmission, line quality has been a paramount consideration. And, even in routine subscriber voice circuits, line quality problems have arisen frequently.
A number of prior approaches are to be found in issued patents. U.S. Pat. No. 3,636,280 to Wetzel exemplifies many of the prior approaches taken to remote disconnect and testing. In Wetzel, a critical signal sent from the central office test board to the remote unit disconnected the customer's equipment and placed a known electrical impedance across the tip and ring wires of the line. A main drawback of the Wetzel contrivance was the complexity of testing equipment and operator skills required to measure the impedance placed across the line being tested. Another significant drawback was that only one test, line impedance, was provided. Loop resistances and line imbalances might well have gone undiscovered at the central office test board.
A variety of remote disconnect units are described in U.S. Pat. No. 3,725,613 to Allen et al, U.S. Pat. No. 3,773,986 to Tremblay, U.S. Pat. No. 4,041,255 to Cambridge et al, and U.S. Pat. No. 3,766,336 to Wikholm. In these patents various signals and circuits were proposed to disconnect the subscriber's equipment. However, the emulation of tests performed by the field troubleshooter and provided by the present invention were not capable of being provided by the remote disconnect units described in these patents.
Other remotely controlled line test devices are described in U.S. Pat. No. 3,739,107 (reissued under U.S. Pat. No. Re29,499) to Spencer, U.S. Pat. No. 4,054,759 to McGrath, U.S. Pat. No. 3,922,508 to Brady, U.S. Pat. No. 3,843,848 to Cox, U.S. Pat. No. 3,663,769 to Boatwright et al, and U.S. Pat. No. 3,790,723 to Stewart. Those devices functioned to provide test conditions and signals in response to remotely transmitted control signals, but are characterized as not only complex but also not particularly closely related to the present invention.